A multi-unit compound stress gradient breeding device and method for large yellow croaker larvae

Abstract

This invention discloses a multi-unit composite stress tiered breeding device and method for juvenile large yellow croaker, belonging to the field of aquaculture breeding technology. The device uses a central control unit as its sole core, forming a fully integrated unidirectional closed-loop drive system. Four independent breeding units are connected through a transparent channel with a centrally located aeration head, forming a physical flow-limiting isolation structure. Each unit independently regulates water temperature, salinity, and dissolved oxygen, creating a multi-factor composite stress gradient. The breeding method employs a three-factor linear equal-gradient synergistic progressive setting, utilizing the juvenile fish's autonomous adaptation and avoidance instincts to achieve cross-unit migration and natural selection. Combined with contour recognition and dynamic tracking algorithms, it monitors the fish population status and mortality rate in real time, and identifies superior offspring with comprehensive stress resistance through secondary verification under extreme stress. This invention offers high screening accuracy and automation, increasing the survival rate of superior individuals by over 40%, reducing labor costs by over 60%, and allowing for flexible adjustment of device parameters. It can be extended to the stress resistance breeding of other marine economic fish species.

Description

Technical Field

[0001] This invention relates to the field of aquaculture breeding technology, and in particular to a multi-unit composite stress tiered breeding device and method for juvenile large yellow croaker. Background Technology

[0002] Large yellow croaker (Larimichthys crocea), one of the most widely farmed marine economic fish species in my country, experiences its juvenile stage as a critical period with the highest environmental sensitivity and mortality rate during its aquaculture cycle. In actual aquaculture production, juvenile fish are highly susceptible to the combined effects of multiple environmental stresses, such as sudden drops in water temperature, drastic fluctuations in salinity, and insufficient dissolved oxygen. Especially during critical stages such as overwintering and seasonal transitions, multiple environmental factors often do not act alone but simultaneously as a complex stress of low temperature, low salinity, and low oxygen, leading to a strong stress response in juvenile fish. This manifests as cessation of feeding, decreased immunity, gill tissue damage, and osmotic pressure imbalance, with mortality rates reaching 30%-50% in severe cases. Even those surviving individuals often exhibit problems such as limited resilience and severely differentiated growth performance after experiencing high-stress environments. Susceptible individuals with rapid growth but high environmental sensitivity are highly prone to large-scale disease outbreaks and deaths when facing complex operational scenarios such as high-density aquaculture, water quality fluctuations, and stocking separation, severely restricting aquaculture efficiency and the large-scale promotion of improved varieties.

[0003] Currently, most domestic and international technical approaches for breeding large yellow croaker to enhance stress resistance rely on screening for single environmental factors. For example, they use only low-temperature tolerance or low-oxygen tolerance as screening indicators, conducting short-term stress experiments under controlled laboratory conditions to select surviving individuals for breeding. This approach has three significant limitations: First, single-factor stress screening fails to reflect the true state of multi-factor synergistic stress in actual aquaculture environments, including temperature, salinity, and dissolved oxygen. While the selected individuals may excel in a single stress trait, they lack comprehensive adaptability to complex stress environments, resulting in insufficient overall stress resistance in actual complex aquaculture scenarios. Second, traditional stress screening devices are mostly single-pond or single-factor control systems, lacking gradient design and connectivity selection mechanisms between multiple independent and controllable aquaculture units. This prevents juvenile fish from being able to adapt to environmental units with varying stress intensities. The selection process relies entirely on manual sorting and experience-based judgment, resulting in low breeding efficiency and poor screening accuracy. Furthermore, existing equipment generally lacks the ability to automatically control multiple environmental parameters in a closed loop and to monitor and warn of fish population status in real time. Stress parameters fluctuate greatly, and responses to abnormal stresses are delayed. This prevents the implementation of an integrated breeding process that combines autonomous selection under multi-factor stress gradients with automatic closed-loop control in abnormal situations. Consequently, the breeding cycle is long, the loss rate of superior individuals is high, and the reproducibility and scalability of the breeding results fail to meet the urgent needs of modern marine aquaculture for widely adaptable and highly resilient breeds. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-unit composite stress tiered breeding device and method for juvenile large yellow croaker, thereby solving the problems in the background art.

[0005] To achieve the above objectives, this invention discloses a multi-unit composite stress tiered breeding device for juvenile large yellow croaker, comprising: The gradient aquaculture zone consists of four independent aquaculture units. Adjacent units are connected by transparent channels with escape-proof nets at both ends, which achieves physical isolation of the water between each aquaculture unit and allows juvenile fish to move freely across units. A small aeration head is installed in the middle of the transparent channel. The aeration head is linked to the dissolved oxygen control parameters of the corresponding aquaculture unit, so that the dissolved oxygen in the channel is consistent with the preset value of the aquaculture unit, eliminating the interference of the channel environment on the juvenile fish's autonomous selection. The environmental control module is equipped with an independent water temperature controller, salinity controller and dissolved oxygen controller for each aquaculture unit. Each controller is electrically connected to the central control unit to realize independent closed-loop control and gradient setting of temperature, salinity and dissolved oxygen parameters for each aquaculture unit. The monitoring and alarm module includes a high-definition waterproof camera installed on the top of each aquaculture unit, and sensors deployed inside the aquaculture unit, including water temperature sensors, salinity sensors and dissolved oxygen sensors, for real-time collection of juvenile fish activity, aggregation distribution, survival status and environmental parameters of each aquaculture unit. The central control unit, as the control core, is electrically connected to the environmental control module and the monitoring and alarm module. It is used to preset the composite stress gradient parameters of each aquaculture unit and, based on the data collected by sensors and cameras, forms a one-way closed-loop control link through closed-loop control algorithm and fish swarm recognition algorithm: when the camera detects that the juvenile fish are static and floating, the real-time mortality rate of a single aquaculture unit is ≥5%, or any sensor detects that the parameter deviates from the set value by ±10%, the central control unit immediately triggers an audible and visual alarm and automatically adjusts the corresponding unit control module to bring the parameter back to the set range.

[0006] Preferably, the size of a single breeding unit is 3m×2m×3m, and the units are connected by a transparent channel with a diameter of 15cm. The length of the transparent channel is 0.15m, and the transparent channel is set at a position 1.5m away from the bottom of the breeding unit.

[0007] Preferably, each aquaculture unit is equipped with an automatic drain valve at the bottom to discharge sewage at fixed times and locations, preventing uneaten feed and feces from spoiling the water and ensuring the long-term stability of the gradient environment.

[0008] Preferably, the basic composite stress gradient for the four aquaculture units is set as follows: Unit 1 (high stress) has a water temperature of 5℃, a salinity of 20‰, and a dissolved oxygen of 5mg / L; Unit 2 (medium-high stress) has a water temperature of 7℃, a salinity of 24‰, and a dissolved oxygen of 6mg / L; Unit 3 (medium stress) has a water temperature of 9℃, a salinity of 28‰, and a dissolved oxygen of 7mg / L; and Unit 4 (low stress control) has a water temperature of 12℃, a salinity of 32‰, and a dissolved oxygen of 9mg / L. Temperature, salinity, and dissolved oxygen are set using a linear, equal-gradient, and progressive logic. The stress intensity increases or decreases synchronously, and the difference between parameters between adjacent units is fixed, forming a gradient combination environment of multi-factor coordinated stress.

[0009] Preferably, the transparent channel has a diameter of 15cm and a smooth inner wall to reduce friction damage to juvenile fish while swimming; the escape-proof nets at both ends of the channel are made of 304 stainless steel with a mesh size of 0.5cm, suitable for juvenile fish with a body length of 3-5cm; each breeding unit has two symmetrically distributed transparent channels, which connect adjacent units to form a two-way communication path between units. The transparent channel has a narrowed flow guiding structure inside, and the escape-proof net forms a grid damping. The transparent channel is equipped with a microbubble air curtain generated by a small aeration head in the middle. The three of them work together to reduce the water convection exchange between adjacent breeding units. The central control unit monitors the water level in real time through the liquid level sensor in each unit and controls the water level difference between each unit to ≤±2mm, so as to eliminate the water gravity exchange caused by the water level difference.

[0010] Preferably, the water temperature controller includes a titanium alloy heating rod and a semiconductor cooling chip; The salinity regulator includes a brine storage tank and an automatic drip peristaltic pump; The dissolved oxygen regulator includes a nano-aeration disc and an oxygen generator; Each control component is independently controlled by the central control unit, enabling closed-loop automatic adjustment of a single aquaculture unit, and the control processes of each unit do not interfere with each other.

[0011] Preferably, the high-definition waterproof camera has a resolution of 1080P and a frame rate of 25fps; the detection accuracies of the water temperature sensor, salinity sensor, and dissolved oxygen sensor are ±0.1℃, ±0.5‰, and ±0.2mg / L, respectively. The central control unit is configured to simultaneously trigger an audible and visual alarm and the corresponding control module when the current unit's real-time mortality rate is ≥5% or any environmental parameter deviates from the set value by ±10%, and automatically revert the parameters to the preset range to achieve closed-loop emergency control in abnormal situations.

[0012] Preferably, the central control unit is equipped with an industrial touch screen, which supports manual preset of composite stress gradient parameters and control threshold modification for each unit, and stores sensor monitoring data and camera image data in real time, and supports one-click data export and full-cycle query of historical records.

[0013] This invention also provides a breeding method based on the above-described device. This device uses a central control unit as the sole core control hub, forming a full-link unidirectional closed-loop drive relationship of signal acquisition, logic judgment, command output, execution feedback, and closed-loop calibration. The breeding method includes the following steps: Step S1, Device Pre-Debugging: 12 hours before the start of breeding, set the temperature, salinity, and dissolved oxygen composite stress gradient parameters of the four breeding units through the central control unit, start the environmental control module of each unit, and wait for the parameters of each breeding unit to stabilize and meet the standards and the equipment to operate without abnormalities before it is ready for use. Step S2, Juvenile Fish Release and Acclimation: Select healthy, disease-free juvenile large yellow croakers with a body length of 3-5cm. After disinfection by soaking in 3‰ saline for 5 minutes, release them into 4 rearing units at a density of 500 fish per unit using a multi-point even release method. After release, close the escape-proof netting and allow 1 hour for environmental adaptation. After the adaptation period, open all escape-proof netting and allow the juvenile fish to move and choose freely between the rearing units. Step S3, Periodic Stress Selection: A 30-day selection cycle is carried out. During this period, the central control unit monitors the environmental parameters and juvenile status of each unit in real time. If any abnormality occurs, an alarm is automatically triggered and the parameters are adjusted to ensure the stability of the compound stress gradient in each unit. The number of juveniles in each unit is recorded at a fixed time every day. The distribution ratio, activity level and growth indicators of the juveniles after they move on their own are statistically analyzed to establish a complete selection data archive. Step S4: Screening of individuals with high stress resistance: After the breeding cycle is completed, priority is given to selecting juvenile fish that have spent more than 70% of their time in Unit 1 (high stress) and Unit 2 (medium-high stress) and whose activity level is stable at level 3. Secondly, individuals that have been clustered in Unit 3 (medium stress) for a long time and whose weight gain rate is ≥0.5g / week are selected as the initial breeding offspring with excellent overall stress resistance. Step S5, Secondary Verification under Extreme Stress: The initially selected superior individuals obtained in Step S4 were placed in an extreme combined stress environment with a water temperature of 5℃, a salinity of 20‰, and a dissolved oxygen of 5mg / L for 48 hours of stress testing. Finally, individuals with a survival rate of ≥90% were identified as offspring with high comprehensive stress resistance.

[0014] Preferably, the full-link unidirectional closed-loop drive relationship of signal acquisition - logic judgment - command output - execution feedback - closed-loop calibration specifically includes: Signal input link: The sensor group and high-definition waterproof camera of the monitoring and alarm module collect environmental parameters and fish status data of each unit in real time at a preset frequency, and transmit them synchronously to the central control unit; Logical judgment link: The central control unit compares and judges the received data through the preset PID closed-loop control algorithm and fish swarm recognition algorithm, checks the matching degree of the data with preset parameters and thresholds, and forms corresponding execution instructions; Command output link: The central control unit sends execution commands to the water temperature, salinity and dissolved oxygen regulators of the corresponding units to complete parameter fine-tuning or emergency control, and simultaneously sends trigger commands to the audible and visual alarm module to trigger the alarm immediately in case of abnormality; Linkage and adaptation rules: The aeration heads in the connecting channel are linked with the dissolved oxygen regulators of the corresponding breeding units, and the dissolved oxygen parameters in the channel are consistent with the preset values ​​of the corresponding units, eliminating the interference of the channel environment on the autonomous selection of juvenile fish.

[0015] Preferably, step S3 also includes a fish mortality identification and counting step: based on the high-definition waterproof camera on the top of the breeding unit, through the "contour recognition + dynamic tracking" algorithm, individuals that are still floating on the water surface or sinking to the bottom of the pond, whose swimming distance is less than 1 body length within 5 consecutive minutes, and who do not swim spontaneously or open and close their gill covers are identified as dead individuals, and are automatically marked and counted; the dynamic tracking algorithm excludes live juvenile fish that are resting due to stress or hibernating at night to avoid misjudgment; Real-time mortality rate per unit = (Number of marked dead individuals in the unit ÷ Total number of juveniles in the unit) × 100%; Total mortality rate of the entire system = (Total number of marked dead individuals in the entire system ÷ Initial total number of tails released) × 100%; When the real-time mortality rate of a single breeding unit is ≥5%, the central control unit will immediately trigger an audible and visual alarm; dead individuals will be manually retrieved during daily sewage discharge for data calibration, and a full inventory will be conducted to lock the final data after the breeding cycle ends.

[0016] Preferably, in step S1, the qualified criteria for gradient adjustment are: the parameters of each unit are stable within ±10% of the preset value through closed-loop control for a long period of time, and the gradient difference between adjacent units is stable; at the same time, the parameter adjustment is set with fixed boundaries, the minimum parameter of the high stress unit is not lower than the 48h half-lethal concentration of large yellow croaker juveniles, the parameter of the low stress control unit does not exceed the optimal growth parameter range of large yellow croaker juveniles, and there is no over-boundary adjustment. In step S3, the activity level grading standard is as follows: Level 1 is static floating, with a swimming distance of less than 1 body length per minute; Level 2 is slow swimming, with a swimming distance of 1-3 body length per minute; Level 3 is normal swimming, with a swimming distance of more than 3 body length per minute. In step S4, individuals with a weight gain rate ≥ 0.5g / week are selected simultaneously, and inferior individuals with strong stress resistance but slow growth are removed, taking into account both the stress resistance and marketability of good breeds.

[0017] Therefore, the present invention has the following beneficial effects: 1. This invention simulates a multi-factor synchronous stress environment in real aquaculture scenarios by combining a gradient of three factors: temperature, salinity, and dissolved oxygen. It leverages the instinct of juvenile fish to seek suitable environments and avoid extreme stress, utilizing interconnected channels to achieve autonomous migration across units and natural selection, eliminating the need for forced manual sorting. This precisely selects individuals with high overall resilience naturally adapted to complex aquaculture environments. Compared to traditional single-factor selection methods, the survival rate of superior individuals in extreme aquaculture environments is increased by more than 40%. Simultaneously, by simultaneously selecting based on growth performance, inferior individuals with strong stress resistance but slow growth are eliminated, significantly improving growth performance and aquaculture stability.

[0018] 2. This device uses a central control unit as the sole core control hub, achieving fully automated operation including PID closed-loop automatic regulation of multiple environmental factor parameters, contour recognition and dynamic tracking of fish school status for real-time intelligent identification, and automatic alarm and emergency control for abnormal situations. It eliminates the need for 24 / 7 human monitoring, significantly reducing breeding labor costs by over 60%. All linkage rules and trigger thresholds are preset before breeding, ensuring a high degree of standardization and replicability in operation, making it suitable for large-scale production demands in high-quality breeding.

[0019] 3. The dimensions of each culture unit and the parameters of the composite stress gradient in this device can be flexibly adjusted through the central controller. The parameter settings boundaries between the high-stress unit and the low-stress control unit are clear, and the gradient difference can be precisely configured according to the breeding objectives. It is not only suitable for the stress resistance breeding of juvenile large yellow croaker with a body length of 3-5cm, but can also be directly extended to the multi-factor stress screening of other marine economic fish. Moreover, the device can effectively maintain the long-term stability of the stress gradient in each unit, and has a wide range of applications, providing a standardized and reusable hardware platform for the promotion of marine fish stress resistance breeding technology.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a gradient aquaculture zone; Figure 2 This is a schematic diagram of a breeding unit; Figure 3 This is a diagram showing the drive connections between the various modules of the device; Figure label: 1. Aquaculture unit; 2. Escape-proof net; 3. High-definition waterproof camera; 4. Transparent channel; 5. Small aeration head; 6. Water temperature controller; 7. Salinity controller; 8. Dissolved oxygen controller; 9. Sewage outlet; 10. Environmental sensor group. Detailed Implementation

[0022] The technical solution of the present invention will be further described below through examples and embodiments.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0025] I. Device Structure This invention discloses a multi-unit composite stress tiered breeding device for juvenile large yellow croaker. The central control unit is the only core control hub, forming a full-link unidirectional closed-loop drive system of "signal acquisition - logic judgment - command output - execution feedback - closed-loop calibration". There is no independent operation logic across modules. All linkage rules and trigger thresholds are preset once before breeding. The entire operation process is automatically controlled in a closed loop without human intervention.

[0026] like Figure 1-2 As shown, the gradient aquaculture zone consists of four independent aquaculture units 1, each measuring 3m × 2m × 3m. Adjacent units are connected by transparent channels 4 with a diameter of 15cm. The inner walls of these channels are smooth to reduce friction damage to juvenile fish. Each aquaculture unit 1 has two symmetrically distributed transparent channels 4, connecting adjacent units to form bidirectional communication paths between units. Escape-proof nets 2 made of 304 stainless steel with a mesh size of 0.5cm are installed at both ends of the channels, suitable for juvenile fish with a body length of 3-5cm. The escape-proof nets 2 allow juvenile fish to freely enter and exit the channels through the mesh, enabling them to swim across units, while preventing them from escaping from the channel openings. The transparent channels 4 have a narrowing flow-guiding structure inside, the escape-proof nets 2 form a mesh damping effect, and a microbubble air curtain generated by small aeration heads 5 is located in the middle of the channels. These three elements work together to reduce water convection and exchange between adjacent aquaculture units 1, achieving a physical flow restriction and isolation effect that allows juvenile fish to pass freely while preventing lateral mixing of water. The central control unit monitors the water level in real time through level sensors in each unit, controlling the water level difference between units to ≤±2mm, completely eliminating water exchange caused by water level differences and reducing the risk of cross-contamination from the source. The small aeration head 5 in the middle of the channel is linked to the dissolved oxygen control parameters of the corresponding aquaculture unit 1, ensuring that the dissolved oxygen in the channel is consistent with the preset value of the unit, eliminating interference from the channel environment on the juvenile fish's autonomous selection.

[0027] The environmental control module includes an independent water temperature controller 6, salinity controller 7, and dissolved oxygen controller 8 for each aquaculture unit.

[0028] The water temperature controller 6 uses a 1.5kW titanium alloy heating rod (resistant to seawater corrosion, with a service life of ≥3 years) and an 800W semiconductor cooling chip. Each unit is equipped with one set, which is installed on the bottom of the side wall of the unit 10cm from the bottom of the pool. It automatically starts and stops through the temperature feedback signal of the central controller, achieving precise control of ±0.1℃ within the range of 5℃-12℃.

[0029] The salinity regulator 7 uses a 50L PP brine storage tank to store 35‰ high-salt solution and 15‰ low-salt solution respectively. It is equipped with a corrosion-resistant peristaltic pump with a flow rate of 0.5L / min. The pump outlet is connected to the middle of the unit water body through a PVC pipe. It automatically adds high-salt or low-salt solution according to the real-time data of the salinity sensor, achieving an adjustment accuracy of ±0.5‰ within the range of 20‰-32‰. The salinity monitoring of each unit adopts dual-sensor backup. When the data deviation between the two sensors exceeds ±0.2‰, an alarm is immediately triggered to avoid monitoring errors affecting the breeding accuracy.

[0030] The dissolved oxygen regulator 8 is equipped with an air compressor with an air output of 20L / min and nano-aeration discs. Two are deployed in each unit, evenly distributed at the bottom of the tank, and connected in series with an oxygen concentration regulating valve. Based on the dissolved oxygen sensor signal, the regulator automatically adjusts the aeration intensity to maintain a stable value within the range of 5mg / L-9mg / L ±0.2mg / L. Each regulator is electrically connected to the central control unit and is independently controlled, enabling independent closed-loop control and gradient setting of temperature, salinity, and dissolved oxygen parameters for each unit. The control processes of each unit do not interfere with each other.

[0031] In terms of water quality control, each unit is equipped with a 10cm diameter drain outlet 9 at the bottom, which drains once a day to promptly remove uneaten food and feces from the bottom; each unit is also equipped with a 30W ultraviolet sterilizer, which runs for 2 hours a day to strictly control the ammonia nitrogen in the water to ≤0.2mg / L and nitrite to ≤0.1mg / L, so as to avoid water quality deterioration from causing additional stress to juvenile fish and to ensure the accuracy of breeding results.

[0032] The monitoring and alarm module includes a high-definition waterproof camera 3 and an environmental sensor group 10.

[0033] The high-definition waterproof camera 3 uses the Hikvision DS-2CD3T26WD-I3 network camera, with 1080P resolution and IP66 waterproof rating. It is installed 1.5m directly above each aquaculture unit, with the lens angle adjusted to cover more than 95% of the water area of ​​the unit. It is connected to the central control unit via network cable to achieve 24-hour continuous recording and real-time image transmission.

[0034] Environmental sensor group 10: The water temperature sensor is model SEN0201 (range -5℃ to 60℃), the salinity sensor is model SEN0161 (range 0‰ to 50‰), and the dissolved oxygen sensor is model SEN0237 (range 0 to 20mg / L), with detection accuracies of ±0.1℃, ±0.5‰, and ±0.2mg / L, respectively. All sensors are fixed at the middle of the side wall of the unit, 20cm from the water surface. The sensor probes are completely submerged and avoid interference from the water flow of the aeration disc. The data sampling frequency is set to 1 time / minute to ensure the real-time and accuracy of the monitoring data.

[0035] The audible and visual alarm uses a DC24V LTE-1101J model, installed next to the central control unit. When the system detects an anomaly, it emits an audible and visual signal of over 80dB. Simultaneously, the central controller's touchscreen displays the abnormal unit number and specific abnormal parameters, facilitating rapid manual location and handling. When the camera detects that the juvenile fish are floating motionless, the real-time mortality rate of a single unit is ≥5%, or any sensor detects a parameter deviation from the set value by ±10%, the central control unit immediately triggers the audible and visual alarm and automatically adjusts the corresponding unit's control module to bring the parameters back to the set range.

[0036] The central control unit uses an Advantech ARK-6320 industrial control computer, equipped with an Intel Core i5 processor, 8GB of memory, and a 10-inch touchscreen display. This central control unit is equipped with gradient control software for the breeding of large yellow croaker under combined stress, and includes parameter setting, real-time monitoring, data storage, historical query, and anomaly alarm modules. The data storage module has a storage period of ≥1 year. Full-cycle breeding data can be exported in Excel format via a USB interface.

[0037] The core supporting algorithms include: a juvenile fish number counting algorithm, which uses "contour recognition + dynamic tracking" technology based on camera images to effectively eliminate interference from uneaten food, bubbles, etc., with a juvenile fish number counting error of ≤±3%; an activity level intelligent recognition algorithm, which analyzes the swimming trajectory and speed of juvenile fish through continuous frame images, automatically completes the activity level classification, and stores the data synchronously; and a parameter closed-loop control algorithm, which adopts PID closed-loop control (proportional-integral-derivative), and adjusts the controller output power in real time according to sensor feedback data to ensure the long-term stability of the composite stress parameters of each unit.

[0038] II. Breeding Methods Based on the above-mentioned device, the method for breeding large yellow croaker juveniles under combined environmental stress according to the present invention includes the following steps: Step S1, Device Pre-Debugging: 12 hours before the start of breeding, the temperature, salinity, and dissolved oxygen composite stress gradient parameters for the four breeding units are set through the central control unit. The basic composite stress gradient for each unit is set as follows: Unit 1 (High Stress): Water temperature 5℃, salinity 20‰, dissolved oxygen 5mg / L; Unit 2 (Medium-High Stress): Water temperature 7℃, salinity 24‰, dissolved oxygen 6mg / L; Unit 3 (Medium Stress): Water temperature 9℃, salinity 28‰, dissolved oxygen 7mg / L; Unit 4 (Low Stress Control): Water temperature 12℃, salinity 32‰, dissolved oxygen 9mg / L. The three parameters of temperature, salinity, and dissolved oxygen are set using a "linear equal gradient coordinated progression" logic, with stress intensity increasing and decreasing synchronously. The parameter differences between adjacent units are fixed. The high stress units are simultaneously set with low temperature, low salinity, and low dissolved oxygen, while the low stress control units are simultaneously set with optimal growth parameters for juvenile fish, completely simulating multi-factor synchronous stress in real aquaculture scenarios. The qualification criteria for gradient adjustment are that the parameters of each unit are consistently stable within ±10% of the preset value through closed-loop control, and the gradient difference between adjacent units is stable. Simultaneously, fixed boundaries are set for parameter adjustment: the minimum parameter concentration in the high-stress unit is no lower than the 48-hour median lethal concentration for juvenile large yellow croaker, and the parameters in the low-stress control unit do not exceed the optimal growth parameter range for juvenile large yellow croaker, with no adjustments exceeding these boundaries. The environmental control modules of each unit are activated, and the equipment is put into standby mode after the parameters of each unit have stabilized and met the standards, and the equipment operates without abnormalities.

[0039] Step S2, Juvenile Fish Release and Acclimation: Select healthy, disease-free large yellow croaker juveniles (3-5cm in length). After disinfection by soaking in 3‰ saline solution for 5 minutes, release them simultaneously into 4 rearing units at a density of 500 juveniles per unit using a multi-point even release method. Each unit has 5 release points: 4 corners and the center, to avoid stress-induced aggregation of juvenile fish. After release, close the escape-proof netting and allow 1 hour for environmental acclimatization. After the acclimatization period, open all escape-proof netting, allowing the juvenile fish to move freely between units.

[0040] Step S3, Periodic Stress Breeding: A 30-day breeding cycle is conducted. During this period, the central control unit monitors the environmental parameters and juvenile status of each unit in real time. Any abnormalities trigger an alarm and adjust parameters automatically to ensure the stability of the combined stress gradient in each unit. The number of juveniles in each unit is recorded at a fixed time each day. The distribution ratio, activity level, and growth indicators of the juveniles after they move independently are statistically analyzed to establish a complete breeding data archive. The activity level grading standards are: Level 1: stationary floating, swimming distance < 1 body length per minute; Level 2: slow swimming, swimming distance 1-3 body length per minute; Level 3: normal swimming, swimming distance > 3 body length per minute.

[0041] The breeding process also includes fish mortality identification and counting: Based on the high-definition waterproof camera on the top of the unit, the "contour recognition + dynamic tracking" algorithm is used to identify individuals that are still floating on the water surface or sinking to the bottom of the pool, whose swimming distance is less than 1 body length within 5 consecutive minutes, and who do not swim or open and close their gill covers as dead individuals, and they are automatically marked and counted; the dynamic tracking algorithm excludes live juvenile fish that are resting due to stress or hibernating at night to avoid misjudgment.

[0042] Real-time mortality rate of a single unit = (number of marked dead individuals in the unit ÷ total number of juvenile fish in the unit) × 100%; cumulative mortality rate of the entire system = (cumulative number of marked dead individuals in the entire system ÷ initial total number of fish) × 100%. When the real-time mortality rate of a single aquaculture unit is ≥ 5%, an audible and visual alarm is immediately triggered in the central control unit; dead individuals are manually retrieved during daily sewage discharge for data calibration, and a full inventory is conducted and the final data is locked after the breeding cycle ends.

[0043] Step S4: Screening of Highly Resilient Individuals: After the breeding cycle is completed, priority is given to selecting juvenile fish that have spent more than 70% of their time in Unit 1 (high stress) and Unit 2 (medium-high stress) and whose activity level is stable at level 3. Secondly, individuals that have been clustered in Unit 3 (medium stress) for a long time and whose weight gain rate is ≥0.5g / week are selected as the initial selection offspring with excellent overall stress resistance. At the same time, inferior individuals with strong stress resistance but slow growth are removed to balance the stress resistance and marketability of the superior breed.

[0044] Step S5, Secondary Verification under Extreme Stress: The initially selected superior individuals obtained in Step S4 were placed in an extreme combined stress environment with a water temperature of 5℃, a salinity of 20‰, and a dissolved oxygen of 5mg / L for 48 hours of stress testing. Finally, individuals with a survival rate of ≥90% were identified as offspring with high comprehensive stress resistance.

[0045] III. Full-link unidirectional closed-loop driving relationship The drive connections between the various modules of the device are as follows: Figure 3 As shown, it specifically includes: Signal input link: The sensor group and high-definition waterproof camera of the monitoring and alarm module collect environmental parameters and fish status data of each unit in real time at a preset frequency, and transmit them synchronously to the central control unit.

[0046] Logical judgment link: The central control unit compares and judges the received data through the preset PID closed-loop control algorithm and fish swarm recognition algorithm, checks the matching degree of the data with preset parameters and thresholds, and forms corresponding execution instructions.

[0047] Command output link: The central control unit sends execution commands to the water temperature, salinity and dissolved oxygen regulators of the corresponding units to complete parameter fine-tuning or emergency control, and simultaneously sends trigger commands to the audible and visual alarm module to trigger the alarm immediately in case of abnormality.

[0048] Linkage and adaptation rules: The aeration heads in the connecting channel are linked with the dissolved oxygen regulators of the corresponding breeding units, and the dissolved oxygen parameters in the channel are consistent with the preset values ​​of the corresponding units, eliminating the interference of the channel environment on the autonomous selection of juvenile fish.

[0049] IV. Implementation Cases Initial conditions: 2000 healthy, disease-free juvenile large yellow croakers (3-5cm in length) were selected and stocked evenly into 4 rearing units, with 500 fish per unit. Initial composite stress parameters were adjusted and stabilized according to the set gradient: Unit 1 (high stress): water temperature 5℃, salinity 20‰, dissolved oxygen 5mg / L; Unit 2 (medium-high stress): water temperature 7℃, salinity 24‰, dissolved oxygen 6mg / L; Unit 3 (medium stress): water temperature 9℃, salinity 28‰, dissolved oxygen 7mg / L; Unit 4 (low stress control): water temperature 12℃, salinity 32‰, dissolved oxygen 9mg / L.

[0050] Process Control: On day 5 of the breeding program, the water temperature in unit 1 (high stress unit) dropped to 4.2℃ due to a malfunction in the cooling element. The sensor detected a deviation from the set threshold, triggering an alarm and automatically activating the backup heater. The water temperature was restored to 5℃ within 30 minutes, with no juvenile deaths reported during this period. On day 15 of the breeding program, the average activity level of juveniles in unit 2 (medium-high stress unit) dropped to level 2. After the system alarm was triggered, manual inspection revealed a salinity of 22‰. The salinity was restored to 24‰ via the central controller, and the juvenile activity level recovered to level 3 12 hours later. Throughout the breeding cycle, all data were recorded daily according to the template, and regular wastewater discharge and water quality control were implemented to ensure a stable breeding process.

[0051] Breeding Results: After a 30-day breeding cycle, the final distribution of juvenile fish in each unit was as follows: Unit 1 (high stress): 320 fish (16%), Unit 2 (medium-high stress): 580 fish (29%), Unit 3 (medium stress): 750 fish (37.5%), and Unit 4 (low stress control): 350 fish (17.5%). 900 juvenile fish that spent over 70% of their time in Units 1 and 2, maintained a stable activity level of 3, and met the weight gain target were selected as superior individuals. Subsequent aquaculture monitoring showed that under complex and combined stress conditions such as low winter temperatures, sudden salinity changes during typhoons, and low oxygen levels in high-density aquaculture, the overall mortality rate of these selected individuals was only 8%, a 77% reduction compared to ordinary cultured juvenile fish (mortality rate 35%). Their overall stress resistance and growth performance were significantly better than traditionally bred individuals, fully meeting the standards for large-scale breeding of superior varieties.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multi-unit compound stress gradient selection device for large yellow croaker larvae, characterized in that, include: The gradient aquaculture zone consists of four independent aquaculture units. Adjacent aquaculture units are connected by transparent channels with escape-proof nets at both ends, achieving physical isolation of the water between each aquaculture unit and allowing juvenile fish to move freely across units. A small aeration head is installed in the middle of the transparent channel. The aeration head is linked to the dissolved oxygen control parameters of the corresponding aquaculture unit, so that the dissolved oxygen in the channel is consistent with the preset value of the aquaculture unit, eliminating the interference of the channel environment on the juvenile fish's autonomous selection. The environmental control module is equipped with an independent water temperature controller, salinity controller and dissolved oxygen controller for each aquaculture unit. Each controller is electrically connected to the central control unit to realize independent closed-loop control and gradient setting of temperature, salinity and dissolved oxygen parameters for each aquaculture unit. The monitoring and alarm module includes a high-definition waterproof camera installed on the top of each aquaculture unit, and sensors deployed inside the aquaculture unit, including water temperature sensors, salinity sensors and dissolved oxygen sensors, for real-time collection of juvenile fish activity, aggregation distribution, survival status and environmental parameters of each aquaculture unit. The central control unit, as the control core, is electrically connected to the environmental control module and the monitoring and alarm module. It is used to preset the composite stress gradient parameters of each aquaculture unit and form a one-way closed-loop control link based on the data collected by sensors and cameras: when the camera detects that the juvenile fish are floating still, the real-time mortality rate of a single aquaculture unit is ≥5%, or any sensor detects that the parameter deviates from the set value by ±10%, the central control unit immediately triggers an audible and visual alarm and automatically adjusts the corresponding aquaculture unit control module to bring the parameters back to the set range.

2. The multi-unit composite stress tiered breeding device for juvenile large yellow croaker according to claim 1, characterized in that, The basic composite stress gradients for the four aquaculture units were set as follows: Unit 1 (high stress) had a water temperature of 5℃, a salinity of 20‰, and dissolved oxygen of 5 mg / L; Unit 2 (medium-high stress) had a water temperature of 7℃, a salinity of 24‰, and dissolved oxygen of 6 mg / L; Unit 3 (medium stress) had a water temperature of 9℃, a salinity of 28‰, and dissolved oxygen of 7 mg / L; and Unit 4 (low stress control) had a water temperature of 12℃, a salinity of 32‰, and dissolved oxygen of 9 mg / L. Temperature, salinity, and dissolved oxygen are set using a linear, equal-gradient, synergistic, and progressive logic. Stress intensity increases or decreases synchronously, and the differences between parameters between adjacent aquaculture units are fixed, forming a gradient combination environment of multi-factor synergistic stress.

3. The multi-unit composite stress tiered breeding device for juvenile large yellow croaker according to claim 1, characterized in that, The transparent channel has a diameter of 15cm and a smooth inner wall to reduce friction damage to juvenile fish while swimming. The escape-proof nets at both ends of the channel are made of 304 stainless steel with a mesh size of 0.5cm, suitable for juvenile fish with a body length of 3-5cm. Each breeding unit has two symmetrically distributed transparent channels, which connect adjacent breeding units to form a two-way communication path between breeding units. The transparent channel has a narrowed flow guiding structure inside, and the escape-proof net forms a grid damping. The transparent channel is equipped with a microbubble air curtain generated by a small aeration head in the middle. The three of them work together to reduce the water convection exchange between adjacent breeding units. The central control unit monitors the water level in real time through the liquid level sensor in each breeding unit and controls the water level difference between each breeding unit to ≤±2mm, so as to eliminate the water gravity exchange caused by the water level difference.

4. The multi-unit composite stress tiered breeding device for juvenile large yellow croaker according to claim 1, characterized in that, The water temperature controller includes a titanium alloy heating element and a semiconductor cooling chip; The salinity regulator includes a brine storage tank and an automatic drip peristaltic pump; The dissolved oxygen regulator includes a nano-aeration disc and an oxygen generator; Each control component is independently controlled by the central control unit, enabling closed-loop automatic adjustment of a single aquaculture unit, and the control processes of each aquaculture unit do not interfere with each other.

5. The multi-unit composite stress tiered breeding device for juvenile large yellow croaker according to claim 4, characterized in that, The high-definition waterproof camera has a resolution of 1080P and a frame rate of 25fps; the detection accuracies of the water temperature sensor, salinity sensor, and dissolved oxygen sensor are ±0.1℃, ±0.5‰, and ±0.2mg / L, respectively. The central control unit is configured to simultaneously trigger an audible and visual alarm and the corresponding control module when the real-time mortality rate of the current breeding unit is ≥5% or any environmental parameter deviates from the set value by ±10%, and automatically restore the parameters to the preset range to achieve closed-loop emergency control of abnormal conditions.

6. The multi-unit composite stress tiered breeding device for juvenile large yellow croaker according to claim 1, characterized in that, The central control unit is equipped with an industrial touch screen, which supports manual preset of composite stress gradient parameters and control thresholds for each breeding unit, and stores sensor monitoring data and camera image data in real time. It also supports one-click data export and full-cycle query of historical records.

7. A method for multi-unit composite stress tiered breeding of juvenile large yellow croaker, characterized in that, The device is implemented based on any one of claims 1-6; the device uses the central control unit as the sole core control hub, forming a full-link unidirectional closed-loop drive relationship of signal acquisition - logic judgment - command output - execution feedback - closed-loop calibration, and the selection method includes the following steps: Step S1, Device Pre-testing: 12 hours before the start of breeding, set the temperature, salinity, and dissolved oxygen composite stress gradient parameters of the four breeding units through the central control unit, start the environmental control module of each breeding unit, and wait until the parameters of each breeding unit are stable and meet the standards and the equipment is running normally before it is ready for use. Step S2, Juvenile Fish Release and Acclimation: Select healthy, disease-free large yellow croaker juveniles with a body length of 3-5cm. After disinfection by soaking in 3‰ saline for 5 minutes, release them into 4 rearing units at a density of 500 fish per unit using a multi-point even release method. After release, close the escape-proof netting and allow 1 hour for environmental adaptation. After the adaptation period, open all escape-proof netting and allow the juvenile fish to move and choose freely between the rearing units. Step S3, Periodic Stress Selection: A 30-day selection cycle is carried out. During this period, the central control unit monitors the environmental parameters and juvenile status of each breeding unit in real time. If any abnormality occurs, an alarm is automatically triggered and the parameters are adjusted to ensure the stability of the compound stress gradient in each breeding unit. The number of juveniles in each breeding unit is recorded at a fixed time every day. The distribution ratio, activity level and growth indicators of the juveniles after they move on their own are statistically analyzed to establish a complete selection data archive. Step S4: Screening of individuals with high stress resistance: After the breeding cycle is completed, priority is given to selecting juvenile fish that have spent more than 70% of their time in Unit 1 (high stress) and Unit 2 (medium-high stress) and whose activity level is stable at level 3. Secondly, individuals that have been clustered in Unit 3 (medium stress) for a long time and whose weight gain rate is ≥0.5g / week are selected as the initial breeding offspring with excellent overall stress resistance. Step S5, Secondary Verification under Extreme Stress: The initially selected superior individuals obtained in Step S4 were placed in an extreme combined stress environment with a water temperature of 5℃, a salinity of 20‰, and a dissolved oxygen of 5mg / L for 48 hours of stress testing. Finally, individuals with a survival rate of ≥90% were identified as offspring with high comprehensive stress resistance.

8. The method for multi-unit composite stress tiered breeding of juvenile large yellow croaker according to claim 7, characterized in that, The full-link unidirectional closed-loop drive relationship of signal acquisition - logic judgment - command output - execution feedback - closed-loop calibration specifically includes: Signal input link: The sensor group and high-definition waterproof camera of the monitoring and alarm module collect environmental parameters and fish status data of each aquaculture unit in real time at a preset frequency, and transmit them synchronously to the central control unit; Logical judgment link: The central control unit compares and judges the received data through the preset PID closed-loop control algorithm and fish swarm recognition algorithm, checks the matching degree of the data with preset parameters and thresholds, and forms corresponding execution instructions; Command output link: The central control unit sends execution commands to the water temperature, salinity and dissolved oxygen regulators of the corresponding aquaculture unit to complete parameter fine-tuning or emergency control, and simultaneously sends trigger commands to the sound and light alarm module to trigger the alarm immediately in case of abnormality; Linkage and adaptation rules: The aeration heads in the connecting channel are linked with the dissolved oxygen regulators of the corresponding aquaculture units, and the dissolved oxygen parameters in the channel are consistent with the preset values ​​of the corresponding aquaculture units, eliminating the interference of the channel environment on the autonomous selection of juvenile fish.

9. The method for multi-unit composite stress tiered breeding of juvenile large yellow croaker according to claim 7, characterized in that, Step S3 also includes fish mortality identification and counting: Based on the high-definition waterproof camera on the top of the breeding unit, the "contour recognition + dynamic tracking" algorithm is used to identify individuals that are still floating on the water surface or sinking to the bottom of the pond, whose swimming distance is less than 1 body length within 5 consecutive minutes, and who do not swim spontaneously or open and close their gill covers as dead individuals, and they are automatically marked and counted; the dynamic tracking algorithm excludes live juvenile fish that are resting due to stress or hibernating at night to avoid misjudgment; Real-time mortality rate per aquaculture unit = (Number of marked dead individuals in the unit ÷ Total number of juvenile fish in the unit) × 100%; Total mortality rate of the entire system = (Total number of marked dead individuals in the entire system ÷ Initial total number of tails released) × 100%; When the real-time mortality rate of a single breeding unit is ≥5%, the central control unit will immediately trigger an audible and visual alarm; dead individuals will be manually retrieved during daily sewage discharge for data calibration, and a full inventory will be conducted to lock the final data after the breeding cycle ends.

10. The method for multi-unit composite stress tiered breeding of juvenile large yellow croaker according to claim 7, characterized in that, In step S1, the qualified criteria for gradient adjustment are: the parameters of each aquaculture unit are stable within ±10% of the preset value through closed-loop control for a long period of time, and the gradient difference between adjacent aquaculture units is stable; at the same time, the parameter adjustment is set with fixed boundaries, the parameters of the high-stress unit are not lower than the 48h half-lethal concentration of large yellow croaker juveniles, the parameters of the low-stress control unit do not exceed the optimal growth parameter range of large yellow croaker juveniles, and there is no over-boundary adjustment. In step S3, the activity level grading standard is as follows: Level 1 is static floating, with a swimming distance of less than 1 body length per minute; Level 2 is slow swimming, with a swimming distance of 1-3 body length per minute; Level 3 is normal swimming, with a swimming distance of more than 3 body length per minute. In step S4, individuals with a weight gain rate ≥ 0.5g / week are selected simultaneously, and inferior individuals with strong stress resistance but slow growth are removed, taking into account both the stress resistance and marketability of good breeds.

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